This invention relates to a high-purity copper sputtering target for the manufacture of thin film deposition materials on semiconductors as in large scale integration and relates also to a thin high-purity copper films of low resistivity obtained by sputtering with such high-purity copper sputtering target.
Aluminum or aluminum alloy (e.g., silicon-containing aluminum) has commonly been used as a wiring material for semiconductor integrated circuits and the like. However, such materials are presenting problems including increased resistance value and electromigration of wirings due to the recent tendencies toward higher degrees of integration which results further miniaturization of elements and the wirings. There have been some attempts to replace aluminum by a refractory metal such as molybdenum or tungsten, but their greater specific resistivities are a drawback.
Attempts have also been made to use copper in place of aluminum to take the advantage of its lower resistivity and greater resistance to electromigration. Nevertheless, pure copper can hardly be employed as a wiring material because it easily oxidizes and is highly reactive with silicon and silicon dioxide films. In the research for the development of copper wiring materials, therefore, emphasis has been laid on an improvement in the oxidation resistance of copper by the controlled addition of another specific element or elements. Most of the researches are directed to the coating of the resulting thin film with an oxide (or nitride) of the added element so as to prevent further oxidation of the film under the coat.
For example, Japanese Patent Application Kokai No. 64-59938 proposes a method which consists of depositing a wiring pattern of an alloy of copper and at least one element chosen from among Ti, Zr, Al, B, and Si, and annealing the deposited wiring pattern in a nitrogen-containing atmosphere whereby a substance that forms the alloy with copper is diffused over the surface to form a nitride barrier.
Patent Application Kokai No. 6-177128 discloses a thin film wiring material of a copper alloy containing 0.02-20 atom % Al or Si. The alloy is oxidized to form an oxide film in which Al or Si is diffused and concentrated on the wiring surface so as to enhance the oxidation resistance of the surface.
A major problem common to the abovementioned methods is an increase in electric resistance by the addition of another element. An increased electric resistance retards signal transmission and adds to the power consumption. For this reason it has been necessary to put an upper limit to the proportion of the additional element so that the electric resistance is as low as that of pure Al, i.e., 2.7 xcexcxcexa9xc2x7cm or less.
As noted above, the efforts to make use of copper as a wiring material have depended largely upon the addition of a specific element, and few attempts have been made to use pure copper itself. However, the recent progress in device structures and barrier materials are altering the situation. For one thing, modern technologies including chemical mechanical polishing (CMP) have simplified device construction and enabled the use of devices with seemingly low oxidation resistance according to ordinary standards. For the other, the development of new barrier materials exclusively designed for copper has raised pure copper to a level high enough for practical use as a wiring material.
Under these circumstances the wiring deposition of pure copper that had been regarded as almost impossible is now rapidly gaining practicality.
In reality, however, the past scanty research on wiring deposition of pure copper has given little impetus to the study of the conditions required of copper wiring material, specially as a material for sputtering target. It should be pointed out, above all, that no copper sputtering target has been developed which has low enough electric resistance for the element that performs high-speed operation for a computer or the like and which is capable of forming a thin film with excellent thickness uniformity.
It is an object of the present invention to provide copper sputtering targets capable of forming wiring deposition films having excellent thickness uniformity as well as the low electric resistance essential for high-speed operation elements and also provide such thin copper films.
After an intensive research, the present inventors have now found that, in order to produce a film of low enough electric resistance, the impurity contents in the target must be kept below certain numerical values. It has also been found necessary to limit down to certain levels the proportions of the elements that have been added for alloying purposes and, if the uniformity of film thickness is to be attained, the dispersions of grain size and crystalline orientation of the target must be controlled.
On the basis of these findings, this invention provides:
1. A high-purity copper sputtering target characterized by comprising up to 0.1 ppm each Na and K, up to 1 ppm each Fe, Ni, Cr, Al, Ca, Mg, up to 5 ppm each carbon and oxygen, up to 1 ppb each U and Th, and, excluding gaseous constituents, more than 99.999% copper.
2. A sputtering target according to 1 above wherein the average grain size on the sputter surface is 250 xcexcm or below And the dispersion of the average grain size from location to location is within plus or minus 20%.
3. A sputtering target according to 1 or 2 above wherein the ratio, I(111)/I(200), of the X-ray diffraction peak intensity I(111) on the (111) plane to the X-ray diffraction peak intensity I(200) on the (200) plane is at least 2.4 and the dispersion of the ratio I(111)/I(200) in the sputter surface is within plus or minus 20%.
4. A sputtering target according to any of 1 to 3 above wherein X-ray diffraction peak width at half height in the sputter surface on the (111) plane is 2xcex8xe2x89xa60.3 deg.
5. A sputtering target according to any of 1 to 4 above wherein it also contains up to 5 ppm each Si, Ag, Ti, Zr, Hf, and B.
6. A sputtering target according to any of 1 to 5 above wherein it has an electric resistance of 1.9 xcexcxcexa9xc2x7cm or less.
7. A thin high-purity copper film characterized by an electric resistance of 2.0 xcexcxcexa9xc2x7cm or less produced by sputtering with a high-purity copper sputtering target according to any of 1 to 6 above.